Some time ago, I found a piece of software that would provide a good guess on the software/algorithm used to save a JPEG.
If I recall correctly, it would analyze something like the compression artifacts and compare it against a known database. The result allowed to know if the JPEG was a result of specific cameras (ie: Canon Powershot A560) or image processing software (ie: Photoshop CS 8.0). Note that it would not read exif information.
What software was this?
Is it still around?
Try JPEGSnoop:
JPEGsnoop is a detailed JPEG image decoder and analysis tool. It reports all image metadata and can even help identify if an image has been edited.
As explained on the JPEGSnoop webpage:
One of the latest features in JPEGsnoop is an internal database that compares an image against a large number of compression signatures. JPEGsnoop reports what digital camera or software was likely used to generate the image.
You can also use Amped Authenticate, which has a richer and user customizable database. It is not a free software, but a professional tool used by law enforcement and forensic labs worldwide. (Disclaimer: I am the company CEO and founder.)
